Filter dyes in a photographic element may be located in a number of locations in the element, such as a radiation-sensitive layer, an overcoat layer, a layer adjacent to a radiation-sensitive layer, an interlayer of a multilayer element, an undercoat layer adjacent to a support, or in a backing layer on the side of the support opposite the radiation-sensitive layer.
When incorporated directly in the radiation-sensitive layer, filter dyes can improve sharpness by absorbing light scattered from one silver halide grain to another. Such dyes are referred to as absorber dyes. Filter dyes also function to retard the sensivitiy of one light sensitive layer relative to another in a multilayer element. By absorbing some of the exposing radiation, the filter dye aids in balancing the sensitivities of all the light sensitive layers.
Filter dyes that function primarily to absorb unwanted radiation due to reflection or refraction from layer interfaces, the layer-support interface, and particularly from the back side of the support, are referred to as antihalation dyes. The layers that contain them are referred to as antihalation layers.
There are a variety of uses for filter dyes and filter layers. For example, a filter layer may be used in or near the overcoat layer to protect the light sensitive layer against radiation from certain spectral regions. In multilayer films where there may be two or more light sensitive layers, it may be necessary to have filter dye interlayers.
It is important that the dyes remain in the layer and not wander or diffuse into the adjacent layers. It is also important for the dyes to be completely decolorized or removed from the element, or both, usually during processing, after having performed their function. Dye stability, especially under high temperature and high humidity incubation is also important. In many cases where absorption of light in a certain spectral region but not the adjacent spectral region is desired it is highly desirable if the filter dye has a steep absorption peak, i.e., the dye is "sharp cutting".
There are a number of problems associated with filter dyes in general and their use in filter layers in photographic elements. Dyes in filter layers can sometimes wander or diffuse into adjacent layers. This can cause problems such as speed loss or stain in the adjacent layers. Filter dyes should be easily decolorized or washed out of the element or both during processing after they have performed their function. When they remain in the element as colored dyes, they cause stain, which adversely affects image quality. This problem can be aggrevated by the use of a polymer mordant in a filter layer to prevent dye wandering.
It is therefore highly desirable to provide a filter dye that has a sharp-cutting absorbance peak, does not wander prior to processing, and washes out easily during processing, leaving little or no residual stain.